Process for forming an aramid copolymer

ABSTRACT

The invention concerns processes for forming polymer crumb comprising residues of 2-(4-amino phenyl)-5 (6) amino benzimidazole (DAPBI), paraphenylene diamine (PPD), and terephthaloyl dichloride (TCl), comprising the steps of: i) forming a slurry of b mole percent DAPBI in a solvent system comprising organic solvent and c weight percent of an inorganic salt, wherein the inorganic salt is present in an amount of at least 5 weight present of the organic solvent; ii) contacting the slurry with a less than stoichiometric amount of terephthaloyl chloride to form an prepolymer solution; and iii) contacting the prepolymer solution with y mole percent of PPD and additional TCL to form a polymer solution; wherein the total amount of TCL added in steps ii) and iii) is a stoichiometric amount based on the total amount of DAPBI and PPD added in steps i) and iii); the DAPBI and PPD are added in an amount sufficient for providing a polymer solution having a weight percent solids of 12 percent or greater on a polymer basis; and wherein the sum of y+b is 100 and the product of b×c is 225 or greater.

TECHNICAL FIELD

The present application concerns methods of producing aramid polymersderived from 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI),para-phenylenediamine (PPD) and terephthaloyl dichloride (TCl) that arecapable of forming fibers having superior physical properties.

BACKGROUND

Fibers derived from 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI),para-phenylenediamine (PPD) and terephthaloyl dichloride (TCl, alsocommonly referred to as terephthaloyl chloride) are known in the art.Such copolymers are the basis for a high strength fibers manufactured inRussia, for example, under the trade names Armos® and Rusar®. See,Russian Patent Application No. 2,045,586. U.S. Pat. No. 4,172,938discloses a process for making aramid polymer that utilizes a solventcontaining at least 1.5 but less than 5 weight percent CaCl₂ inN-methyl-2-pyrrolidone (NMP).

Present technology does not permit producing DAPBI-containing aramidpolymers in a high solids content reaction while achieving polymerhaving high inherent viscosity. Such a process would be desirable.

SUMMARY

In some aspects, the invention concerns processes for forming polymercrumb comprising residues of 2-(4-amino phenyl)-5 (6) aminobenzimidazole (DAPBI), paraphenylene diamine (PPD), and terephthaloyldichloride (TCl), comprising the steps of: i) forming a slurry of b molepercent DAPBI in a solvent system comprising organic solvent and cweight percent of an inorganic salt, wherein the inorganic salt ispresent in an amount of at least 5 weight percent of the organicsolvent; ii) contacting the slurry with a less than stoichiometricamount of terephthaloyl chloride, based on the amount of DAPBI in stepi), to form an prepolymer solution; and iii) contacting the prepolymersolution with y mole percent of PPD and additional TCL to form a polymersolution; wherein the total amount of TCL added in steps ii) and iii) isa stoichiometric amount based on the total amount of DAPBI and PPD addedin steps i) and iii); wherein the DAPBI and PPD is added in an amountsufficient for providing a polymer solution having a weight percentsolids of 12 percent or greater on a polymer basis; and wherein the sumof y+b is 100 and the product of b×c is 225 or greater. In someembodiments, b×c is 300 or 350 or greater.

In other aspects, the invention relates to a polymer comprising residuesof 2-(4-amino phenyl)-5 (6) amino benzimidazole (DAPBI), paraphenylenediamine (PPD), and terephthaloyl dichloride (TCl) made by the processesof the invention described herein. The polymer may be in such forms as apolymer crumb or polymer powder. In one embodiment, a polymer and/orpolymer crumb is made by a process comprising the steps of i) forming aslurry of b mole percent DAPBI in a solvent system comprising organicsolvent and c weight percent of an inorganic salt, wherein the inorganicsalt is present in an amount of at least 5 weight percent of the organicsolvent; ii) contacting the slurry with a less than stoichiometricamount of terephthaloyl chloride, based on the amount of DAPBI in stepi), to form an prepolymer solution; and iii) contacting the prepolymersolution with y mole percent of PPD and additional TCL to form a polymersolution; wherein the total amount of TCL added in steps ii) and iii) isa stoichiometric amount based on the total amount of DAPBI and PPD addedin steps i) and iii); wherein the DAPBI and PPD is added in an amountsufficient for providing a polymer solution having a weight percentsolids of 12 percent or greater on a polymer basis; and wherein the sumof y+b is 100 and the product of b×c is 225 or greater. In someembodiments, b×c is 300 or 350 or greater. In other embodiments, theDAPBI and PPD are present in a molar ratio in the range of from 0.25 to4. In yet other embodiments, the polymer produced has an inherentviscosity of 4 dl/g or greater. In some preferred embodiments, thepolymer has an inherent viscosity of 4 to 8 dl/g; in some embodimentsthe polymer has an inherent viscosity of 6 dl/g or greater.

The use of higher amounts of inorganic salt (such as CaCl₂) has led to asurprising increase in inherent viscosity (at higher solids). Thishigher inherent viscosity is of utility when producing high molecularweight materials such as fibers. Furthermore, the higher solids contentof the polymerization solution reduces costs of manufacture as comparedwith lower solids reactions.

In some embodiments, there is more than one addition of terephthaloyldichloride in step ii). In some embodiments there are three additions.In some reactions, before and/or after each addition of terephthaloyldichloride in step ii), the slurry or prepolymer solution is cooled to atemperature of 20° C. or below, or 15° C. or below. In certain preferredembodiments, all of the steps are performed under agitation. In someprocesses, no more than 10 percent of the terephthaloyl dichloride isadded in any single addition up to the gel point. The final addition ofterephthaloyl dichloride can be done as a single amount so as to allowmixing prior to gelation

In certain embodiments, the prepolymer solution in step iii) is alsocooled to a temperature of 20° C. or below, or 15° C. or below, prior tocontacting the slurry with terephthaloyl dichloride. It can be similarlycooled after the addition.

In some embodiments, the organic solvent is N-methyl-2-pyrrolidone (NMP)or dimethylacetamide (DMAC). Suitable inorganic salts include LiCl andCaCl₂. In some embodiments, the solvent has an inorganic salt weightpercent in the range of from 5.0 to 10%.

The polymer can be isolated from the solution (that is, the polymerizingsolvent) in some embodiments. The polymer can be further treated withone or more washing steps, neutralizing steps, or both. In someembodiments, the polymer can be comminuted. The washing and/orneutralizing steps can be performed before or after comminuting thepolymer.

In some aspects, the invention additionally concerns the step ofdissolving the polymer in a solvent comprising sulfuric acid to form asolution suitable for spinning fibers. The polymer to be dissolvedincludes the isolated polymer that may, or may not have been, washedand/or neutralized and the polymer may or may not have been comminuted.

In some embodiments, the total amount of DAPBI and PPD used in thepolymer are present in a molar ratio in the range of from 0.25 to 4. Forcertain processes, the amount of DAPBI use to form the slurry in step i)is in the range of from 2 to 9 weight percent. For certain processes,the amount of PPD used to form the polymer solution in step iii) is from0.8 to 6.0 weight percent.

The processes of the invention can be run at high solids content. Insome embodiments, the weight percent solids in the polymer solution is12-15% on a polymer basis. In some processes, the weight percent solidsin the polymer solution is 14-25% on a monomer basis. In someembodiments, the weight percent solids in the polymer solution is 14-19%on a monomer basis.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In some aspects, the concerns processes for forming polymer crumbcomprising residues of 2-(4-amino phenyl)-5 (6) amino benzimidazole(DAPBI), paraphenylene diamine (PPD), and terephthaloyl dichloride(TCl), comprising the steps of: i) forming a slurry of b mole percentDAPBI in a solvent system comprising organic solvent and c weightpercent of an inorganic salt, wherein the inorganic salt is present inan amount of at least 5 weight present of the organic solvent; ii)contacting the slurry with a less than stoichiometric amount ofterephthaloyl chloride, based on the amount of DAPBI in step i), to forman prepolymer solution; and iii) contacting the prepolymer solution withy mole percent of PPD and additional TCl to form a polymer solution;wherein the total amount of TCl added in steps ii) and iii) is astoichiometric amount based on the total amount of DAPBI added in stepi) and PPD added in step iii); the DAPBI and PPD is added in an amountsufficient for providing a polymer solution having a weight percentsolids of 12 percent or greater on a polymer basis; and wherein the sumof y+b is 100 and the product of b×c is 225 or greater. This stepwiseprocess provides a process for making a polymer by reacting a firstdiamine (DAPBI) with TCl without competition from a second diamine, atleast initially in the polymerization. The oligomer solution that isformed is then allowed to react with the second diamine (PPD) andadditional TCl. If both diamines (DAPBI & PPD) were simply combined withthe TCl initially, they would uncontrollably compete with each otherduring the reaction.

Vessels useful for producing polymers, and temperatures and otherconditions useful in producing polymers, include, for example, detailsdisclosed in such patents as U.S. Pat. No. 3,063,966 to Kwolek et al.;U.S. Pat. No. 3,600,350 to Kwolek; U.S. Pat. No. 4,018,735 to Nakagawaet al.; U.S. Pat. No. 5,646,234 to Jung et al.; U.S. Pat. No. 4,172,938to Mera; and WO2005054337 to Bos.

The solvent system has an inorganic salt content of at least 5 weightpercent, based on the combination of solvent and salt. In someembodiments, it is believed the inorganic salt content can be as high as12 weight percent. In some preferred embodiments the inorganic saltcontent is no more than 10 weight percent and in some most preferredembodiments the content is no more than 8 weight percent. Preferredorganic solvents include N-methyl-2-pyrrolidone (NMP), dimethylacetamide(DMAC), or mixtures thereof. Preferred inorganic salts include LiCl,CaCl₂ and mixtures thereof.

In one preferred embodiment, the solvent system is NMP/CaCl₂. In certainembodiments, the NMP/CaCl₂ solvent has a CaCl₂ weight percent in therange of from 5 to 10%; in some embodiments the range is 5 to 8 weight%. It should be noted that the solubility of CaCl₂ in NMP is about 8%.As such when more than 8% CaCl₂ is used, some undissolved CaCl₂ ispresent in the solvent system. The solvents and salts can be obtainedfrom commercial sources and, if desired, purified by methods known tothose skilled in the art.

In some processes, the molar ratio of DAPBI to PPD is in the range offrom 0.25 to 4.0. This ratio is equivalent to a DAPBI/PPD ratio of 20/80to 80/20. In certain processes, the amount of the slurry that is DAPBIin step (i) is in the range of from 2.0 to 9 weight percent of theslurry.

In some embodiments, the polymer crumb is made by copolymerizing aprepolymer solution containing oligomers formed from b mole % DAPBI andless than a stoichiometric amount of TCl with y mole % PPD andadditional TCl in a mixture of organic solvent containing c weightpercent of inorganic salt. In preferred embodiments, the sole aminemonomers used in the polymerization are PPD and DAPBI. In someembodiments other amine monomers can be present; however, PPD and DAPBIare present in such embodiments such that y+b equals 100, based on therelative amounts of PPD and DAPBI used. The product of b×c is 225 orgreater. In some embodiments, the product of b×c is 300 or greater andpreferably 350 or greater.

In some embodiments, the weight percent solids in the product solutionis 12-15% on a polymer basis. The term “solids” is well known in the artto refer to the polymer in the product/polymer solution. By “polymerbasis” it is meant the weight of the polymer divided by the weight ofthe total solution of polymer and solvent (and reaction byproducts),expressed as a percentage. By “monomer basis” it is meant the sum of theweights of the individual monomers divided by the weight of the totalsolution of polymer and solvent (and any reaction byproducts), expressedas a percentage. In some processes, the weight percent solids in theproduct solution is 14-25% on a monomer basis. In some embodiments, theweight percent solids in the product solution is 14-19% on a monomerbasis.

In some embodiments, one or more, or all of the process steps can beperformed under agitation.

The polymer can be isolated from the solvent, and in some embodimentsthe invention concerns a polymer powder comprising residues of2-(4-amino phenyl)-5 (6) amino benzimidazole (DAPBI), paraphenylenediamine, and terephthaloyl dichloride. In some embodiments, the polymerpowder has an inherent viscosity of 4 dl/g or greater. In some preferredembodiments, the polymer has an inherent viscosity of 4 to 8 dl/g; insome embodiments the polymer has an inherent viscosity of 6 dl/g orgreater.

The isolated polymer can be comminuted to a desired particle size toassist in processing and storage. The polymer can be treated with one ormore washing steps, neutralizing steps, or both. These washing and/orneutralizing steps can be performed before or after comminuting thepolymer. Equipment suitable for use in agitation of the reactionmixtures, washing and neutralization steps, and comminuting the polymeris known to those skilled in the art.

Molecular weights of polymers are typically monitored by, and correlatedto, one or more dilute solution viscosity measurements. Accordingly,dilute solution measurements of the relative viscosity (“V_(rel)” or“η_(rel)” or “n_(rel)”) and inherent viscosity (“V_(inh)” or “η_(inh)”or “n_(inh)”) are typically used for monitoring polymer molecularweight. The relative and inherent viscosities of dilute polymersolutions are related according to the expression

V _(inh) =ln(V _(rel))/C,

where in is the natural logarithm function and C is the concentration ofthe polymer solution. V_(rel) is a unitless ratio, thus V_(inh) isexpressed in units of inverse concentration, typically as deciliters pergram (“dl/g”).

Neutralization of the polymer can occur in one or more steps bycontacting the polymer with a base. Suitable bases include NaOH; KOH;Na₂CO₃; NaHCO₃; NH₄OH; Ca(OH)₂; K₂CO₃; KHCO₃; or trialkylamines,preferably tributylamine; other amines; or mixtures thereof. In oneembodiment, the base is water soluble. In some preferred examples theneutralization solution is an aqueous solution of base.

The polymer can also be washed with water independent of or prior toand/or after the neutralization step.

In some aspects, the invention additionally concerns the step ofdissolving the polymer in a solvent comprising sulfuric acid to form asolution suitable for spinning fibers (also referred to as a “spindope”). The polymer to be dissolved includes the isolated polymer thatmay or may not have been washed and/or neutralized and the polymer mayor may not have been comminuted. While any suitable solvent can be usedto dissolve the polymer, in some embodiments the solvent comprisesN-methyl-2-pyrrolidone (NMP) or dimethylacetamide (DMAC) and aninorganic salt to form a solution suitable for spinning fibers. Thedissolved polymer can be spun into fibers by conventional techniquesknown to those skilled in the art.

The spin dope containing the copolymer described herein can be spun intodope filaments using any number of processes; however, wet spinning and“air-gap” spinning are the best known. The general arrangement of thespinnerets and baths for these spinning processes is well known in theart, with the figures in U.S. Pat. Nos. 3,227,793; 3,414,645; 3,767,756;and 5,667,743 being illustrative of such spinning processes for highstrength polymers. In “air-gap” spinning the spinneret typicallyextrudes the fiber first into a gas, such as air, prior to beingcoagulated in a aqueous bath. This is a preferred method for formingfilaments and sulfuric acid is the preferred spin solvent for thisprocess.

As used herein, the terms filaments and fibers are used interchangeably.

The fiber can be contacted with one or more washing baths or cabinets.Washes can be accomplished by immersing the fiber into a bath or byspraying the fiber with the aqueous solution. Washing cabinets typicallycomprise an enclosed cabinet containing one or more rolls that the yarntravels around a number of times, and across, prior to exiting thecabinet. As the yarn travels around the roll, it is sprayed with awashing fluid. The washing fluid is continuously collected in the bottomof the cabinet and drained therefrom.

The temperature of the washing fluid(s) is preferably greater than 30°C. The washing fluid can also be applied in vapor form (steam), but ismore conveniently used in liquid form. Preferably, a number of washingbaths or cabinets are used. The residence time of the yarn in any onewashing bath or cabinet will depend on the desired concentration ofresidual sulfur in the yarn. In a continuous process, the duration ofthe entire washing process in the preferred multiple washing bath(s)and/or cabinet(s) is preferably no greater than about 10 minutes, morepreferably greater than about 5 seconds. In some embodiments theduration of the entire washing process is 20 seconds or more; in someembodiments the entire washing is accomplished in 400 seconds or less.In a batch process, the duration of the entire washing process can be onthe order of hours, as much as 12 to 24 hours or more.

If needed, the acidic spin solvent can be removed from the fiber by in abath or a cabinet. For example, neutralization of the acid (such assulfuric acid solvent) in the yarn by a base can occur in a bath or acabinet. In some embodiments, the neutralization bath or cabinet canfollow one or more washing other baths or cabinets. Washes can beaccomplished by immersing the fiber into a bath or by spraying the fiberwith the aqueous solution. Neutralization can occur in one bath orcabinet or in multiple baths or cabinets. In some embodiments, preferredbases for the neutralization of sulfuric acid impurity include NaOH;KOH; Na₂CO₃; NaHCO₃; NH₄OH; Ca(OH)₂; K₂CO₃; KHCO₃; or trialkylamines,preferably tributylamine; other amines; or mixtures thereof. In oneembodiment, the base is water soluble. In some preferred examples theneutralization solution is an aqueous solution containing 0.01 to 1.25mols of base per liter, preferably 0.01 to 0.5 mols of base per liter.The amount of cation is also dependent on the time and temperature ofexposure to the base and the washing method. In some preferredembodiments, the base is NaOH or Ca(OH)₂.

After treating the fiber with base, the process optionally can includethe step of contacting the yarn with a washing solution containing wateror an acid to remove all or substantially all excess base. This washingsolution can be applied in one or more washing baths or cabinets.

After washing and neutralization, the fiber or yarn can be dried in adryer to remove water and other liquids. One or more dryers can be used.In certain embodiments, the dryer can be an oven that uses heated air todry the fibers. In other embodiments, heated rolls can be used to heatthe fibers. The fiber is heated in the dryer to a temperature of atleast about 20° C. but less than about 100° C. until the moisturecontent of the fiber is 20 weight percent of the fiber or less. In someembodiments the fiber is heated to 85° C. or less. In some embodimentsthe fiber is heated under those conditions until the moisture content ofthe fiber is 14 weight percent of the fiber or less. In someembodiments, the fiber is heated at least to about 30° C.; in someembodiments the fiber is heated at least to about 40° C.

The dryer residence time is less than ten minutes and is preferably lessthan 180 seconds. The dryer can be provided with a nitrogen or othernon-reactive atmosphere. The drying step typically is performed atatmospheric pressure. If desired, however, the step can be performedunder reduced pressure. In one embodiment, the filaments are dried undera tension of at least 0.1 gpd, preferably a tension of 2 gpd or greater.

Definitions

As used herein, the term “residue” of a chemical species refers to themoiety that is the resulting product of the chemical species in aparticular reaction scheme or subsequent formulation or chemicalproduct, regardless of whether the moiety is actually obtained from thechemical species. Thus, a copolymer comprising residues of paraphenylenediamine refers to a copolymer having one or more units of the formula:

Similarly, a copolymer comprising residues of DAPBI contains one or moreunits of the structure:

A copolymer having residues of terephthaloyl dichloride contains one ormore units of the formula:

The term “polymer,” as used herein, means a polymeric compound preparedby polymerizing monomers, whether of the same or a different type. Theterm “copolymer” (which refers to polymers prepared from two differentmonomers), the term “terpolymer” (which refers to polymers prepared fromthree different types of monomers), and the term “quadpolymer (whichrefers to polymers having four different types of monomers) are includedin the definition of polymer.

The term “crumb” means the polymer has breakable clumps or particlesthat generally have an effective particle diameter of greater than 100micronmeters, sometimes greater than 1 mm. In some embodiments, crumbfurther includes coarse powders having an effective particle diameter of1000 micrometers or less. Effective particle diameter is the diameter ofa circle with area equal to that of the projection of the particle on aplane. The term “powder” when referring to polymer means particles ofthe copolymer having neither fibrous qualities like fiber or pulp, norfibrous film-like qualities like fibrids. Individual particles tend tobe fibril-free, have a random shape, and in some embodiments have aneffective particle diameter of 840 micrometers or less. U.S. Pat. Nos.5,474,842 and 5,811,042 are illustrative.

As used herein, “stoichiometric amount” means the amount of a componenttheoretically needed to react with all of the reactive groups of asecond component. For example, “stoichiometric amount” refers to themoles of terephthaloyl dichloride needed to react with substantially allof the amine groups of the amine components (such as PPD and/or DAPBI)in any one step or in the overall reaction. It is understood by thoseskilled in the art that the term “stoichiometric amount” refers to arange of amounts that are typically within 10% of the theoreticalamount. For example, for the total reaction, the stoichiometric amountof terephthaloyl dichloride used in a polymerization reaction can be90-110% of the amount of terephthaloyl dichloride theoretically neededto react with total amount of all the amine groups used in the variousadditions of PPD and DAPBI.

The term “fiber” refers to a relatively flexible, macroscopicallyhomogeneous body having a high ratio of length to width across itscross-sectional area perpendicular to its length.

The term “organic solvent” is understood herein to include a singlecomponent organic solvent or a mixture of two or more organic solvents.In some embodiments, the organic solvent is dimethylformamide,dimethylacetamide (DMAC), N-methyl-2-pyrrolidone (NMP), ordimethylsulfoxide. In some preferred embodiments, the organic solvent isN-methyl-2-pyrrolidone or dimethylacetamide.

The term “inorganic salt” refers to a single inorganic salt or to amixture of two or more inorganic salts. In some embodiments, theinorganic salt is sufficiently soluble in the solvent and liberates anion of a halogen atom. In some embodiments, the preferred inorganic saltis KCl, ZnCl₂, LiCl or CaCl₂. In certain preferred embodiments, theinorganic salt is LiCl or CaCl₂.

By “never-dried” it is meant the moisture content of the fiber is atleast 75 weight percent of the fiber.

As used in the specification including the appended claims, the singularforms “a,” “an,” and “the” include the plural, and reference to aparticular numerical value includes at least that particular value,unless the context clearly dictates otherwise. When a range of values isexpressed, another embodiment includes from the one particular valueand/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another embodiment. Allranges are inclusive and combinable. When any variable occurs more thanone time in any constituent or in any formula, its definition in eachoccurrence is independent of its definition at every other occurrence.Combinations of substituents and/or variables are permissible only ifsuch combinations result in stable compounds.

The invention is illustrated by the following examples, which are notintended to be limiting in nature.

Test Methods

Inherent viscosity can be determined using a solution in which a polymeris dissolved in a concentrated sulfuric acid with a concentration of 96wt % at a polymer concentration (C) of 0.5 g/dl and at a temperature of25° C. Inherent viscosity is then calculated as ln (t_(poly)/t_(solv))/Cwhere t_(poly) is the drop time for the polymer solution and t_(solv) isthe drop time of the pure solvent.

EXAMPLES

NMP, CaCl₂, DAPBI, PPD, and TCl were obtained from commercial sources.

Example 1

31.82 kg of NMP Solvent containing 5.38% CaCl₂ (a “c” value of 5.38) ischarged to a FM130D Littleford Reactor. 2180 g of DAPBI (a “b” value of70) is then charged. The contents are then cooled to 10° C. 707 g ofterephthaloyl chloride is charged to form a prepolymer solution. Theprepolymer solution is then cooled to 10 C and 455 g of PPD (an “y”value of 30) is dissolved into the prepolymer mixture. 2122 g ofterephthaloyl dichloride is then added. The polymer product of (b×c)equals 377.

Solids in this reaction are 12% on a polymer basis and 14.7% on a totalmonomer basis. Final inherent viscosity is 6.5 dl/g.

Comparison Example 1

31.82 kg of NMP Solvent containing 2.94% CaCl₂ (a “c” value of 2.94) wascharged to a FM130D Littleford Reactor. 456 g of PPD (an “y” value of30) and 2200 g of DAPBI (a “b” value of 70) were then charged. Processwas then cooled to 7° C. Three additions of terephthaloyl dichloridewere made: 997 g, 997 g, and 855 g. After the first addition, themixture was cooled to 7 C and after the second the mixture was cooled to11° C. On conclusion of reaction, the reactor was inspected fordeposits, no large chunks of DAPBI were observed on the wall. Theproduct of (b×c) was equal to 206.

Solids in this reaction were 12% on a polymer basis and 14.7% on a totalmonomer basis. Final inherent viscosity was 3.9 dl/g.

Comparison Example 2

31.82 kg of NMP Solvent containing 3.91% CaCl₂ (a “c” value of 3.91) wascharged to a FM130D Littleford Reactor. 455 g of PPD (an “y” value of30) and 2202 g of DAPBI (a “b” value of 70) were then charged. Processwas then cooled to 8° C. Three additions of terephthaloyl dihloride weremade: 997 g, 997 g, and 853 g. After the first addition, the mixture wascooled to 10 C and after the second the mixture was cooled to 12° C. Onconclusion of reaction, the reactor was inspected for deposits, no largechunks of DAPBI were observed on the wall. The product of (b×c) wasequal to 274.

Solids in this reaction were 12% on a polymer basis and 14.7% on a totalmonomer basis. Final inherent viscosity was 4.6 dl/g.

Example 2

Example 1 is repeated, however the terephthaloyl dichloride is added tothe DAPBI in three additions. After each addition, the mixture is cooledto 10 C. A polymer solution and polymer similar to Example 1 is theresult. cl Example 3

The polymers of Examples 1 and 2 are individually combined with either(1) a solvent comprising sulfuric acid or (2) a solvent comprisingN-methyl-2-pyrrolidone (NMP) or dimethylacetamide (DMAC) and aninorganic salt. The combination is agitated, while cooling if needed tocontrol temperature, until the polymer is fully dissolved in the solventand a solution suitable for spinning fibers is formed. The polymersolution containing sulfuric acid is extruded through a spinneret andair-gap spun and spun into a coagulation bath that forms filaments thatare washed, are dried, and are wound on a bobbin. The polymer solutioncontaining NMP or DMAC is extruded through a spinneret and wet spun in acoagulation bath that forms filaments that are washed, are dried, andare wound on a bobbin.

What is claimed:
 1. A polymer comprising residues of 2-(4-aminophenyl)-5(6) amino benzimidazole (DAPBI), paraphenylene diamine (PPD)and terephthaloyl chloride (TCL), made by a process comprising the stepsof: i) forming a slurry of b mole percent DAPBI in a solvent systemcomprising organic solvent and c weight percent of an inorganic salt,wherein the inorganic salt is present in an amount of at least 5 weightpresent of the organic solvent; ii) contacting the slurry with a lessthan stoichiometric amount of terephthaloyl chloride, based on theamount of DAPBI in step i), to form an prepolymer solution; and iii)contacting the prepolymer solution with y mole percent of PPD andadditional TCL to form a polymer solution; wherein the total amount ofTCL added in steps ii) and iii) is a stoichiometric amount based on thetotal amount of DAPBI added in step i) and PPD added in step iii);wherein the DAPBI and PPD are added in an amount sufficient forproviding a polymer solution having a weight percent solids of 12percent or greater on a polymer basis; and wherein the sum of y+b is 100and the product of b×c is 225 or greater.
 2. The polymer of claim 1wherein the product of (b×c) is equal to 300 or greater.
 3. The polymerof claim 2 wherein the product of (b×c) is equal to 350 or greater. 4.The polymer of claim 1 wherein the DAPBI and PPD are present in a molarratio in the range of from 0.25 to
 4. 5. The polymer of claim 1 whereinthe polymer has an inherent viscosity of 4 dl/g or greater.
 6. Thepolymer of claim 1 in the form of a crumb.